3D Touch Calibration Procedure
3D Touch is a pressure sensing technology embedded within the iPhone 6s and later. If a device's display is acting up, or has been recently repaired, it must be recalibrated using the 3D Touch Calibration Procedure.
This procedure is a very delicate one, and can only be performed by an Apple authorized technician on iPhone 6s and later.
The device being calibrated must be running a public release of iOS 10.0 or later. A device running iOS 9 or earlier will be irreparably damaged by the fixture if it is not updated first. It must be awake on the lock screen or the home screen prior to beginning the procedure, and have at least 20% battery remaining.
Additionally, the technician must have a back-of-house (BOH) Mac running the latest version of 3DTouchCal software, and a 3D Touch Calibration Fixture.
Often called Horizon machines due to their codename, 3D Touch Calibration Fixtures have the ability to calibrate the display, proximity sensor, and pressure sensors on iPhone 6s or later. They can also pair new Touch ID buttons to a Secure Enclave Processor. They are not to be confused with Display Calibration Fixtures, which are used with iPhone 5 through iPhone 6 Plus during the Display Calibration Procedure.
Finally, the device to be calibrated must be wiped clean with a lint-free microfiber cloth and placed in a cradle, if required, based upon the device's size. If the device's display is not perfectly clean, fingerprints and other oils will damage the pads on the Calibration Fixture and render it useless for accurate calibration until they are replaced. Once the cradle and/or device are locked securely in place, the iPhone must be connected to the Calibration Fixture via the Device-Under-Test (DUT) cable. If required, the technician can place an included speaker port cover on the device to reduce noise generated during calibration.
The technician must power on the Calibration Fixture and confirm it is connected to the host Mac. Then, the technician will launch the 3DTouchCal software. 3DTouchCal will begin to prepare the device for calibration by searching an internal service called Display Cloud for display calibration data. Once it is found, calibration begins.
The calibration process takes around fifteen minutes. The Calibration Fixture is not to be opened during this time, even though it has built-in safety precautions if this happens.
During calibration, the device is wiped and flashed with a specialized firmware specifically for calibration, similar to Factory Firmware. The display will mostly remain white, and may flash a few test patterns.
Once calibration is complete, the device is wiped again and restored to the latest version of iOS. 3DTouchCal will display a green check mark if calibration succeeds, and a red cross if it fails. If calibration fails, 3DTouchCal will display instructions to resolve the issue, if applicable.
At this point, the 3D Touch display and proximity sensor are calibrated. The Calibration Fixture is opened and the DUT cable detached. The device is removed and speaker port cover discarded, if applicable.